Thank you.
My subjective impression of added surround processing is that it can add a sense of "spaciousness", but at the cost of "clarity" and "focus". If one's speakers are cheap and lack clarity, the cost might not be too high, and the added spaciousness may make it all seem worthwhile.
In the case of using DPL II to decode DPL I material, my subjective impression is that it sometimes sounds better, sometimes about the same, and sometimes worse, which can all happen in the same movie at different places in the soundtrack. It is the worse times that keep me from using it, as the worse, to me, sounds very wrong. That, of course, should be no surprise, as it is redirecting (aka misdirecting) some of the front channel sounds to the rear, so things are not being placed where they should be placed. When it is wrong, it is just plain bad, in my opinion. In those cases where DPL II subjectively sounds better, DPL I does not sound wrong, so the gain is not as much as the cost, in my opinion. Obviously, most people seem to perfer having things misdirected with DPL II, so it would hardly be surprising if most of the people who read this have a different opinion on the matter.
For those interested in reading about how DPL works, you might want to read:
http://forums.audioholics.com/forums/showpost.php?p=395470&postcount=28
